Soil Mineral Nitrogen Research Articles

Response of Soil Net Nitrogen Mineralization to a Litter in Three Subalpine Forests

Forest litter accumulation can regulate the soil microclimate and alter nutrient distribution, but the effects of litter quality and seasonal differences on soil nitrogen (N) mineralization are still uncertain. The effects of litter change on the rates of net N mineralization, nitrification, and ammonification were studied through in situ incubation experiments in coniferous, mixed, and broad-leaved forests in the eastern Qinghai–Tibetan Plateau. Two litter treatments were established, one to allow the litter to enter the soil normally (remain litter) and the other to prevent the litter from entering the soil (remove litter). Soil samples were collected at the freezing (FS), thawing (TS), early growing (EGS), late growing (LGS), and early freezing (EFS) seasons during the 1.5-year incubation period. Compared to coniferous forests, the effects of litter removal on the net ammonification, nitrification, and N mineralization rates were more pronounced in broad-leaved forests, mainly during the growing and thawing seasons. Structural equation modeling indicated that microbial biomass N (MBN) was a common factor affecting the net ammonification, nitrification, and N mineralization rates in the three forest soils. The coniferous forest microbial biomass carbon (MBC), mixed forest soil moisture, broad-leaved forest soil N concentration, and C:N ratio were the unique influencing factors of the different forest types. The results showed that the effect of litter distribution on the soil net N mineralization mainly depended on forest type and season, suggesting that the litter composition and productivity in different seasons and forest types may alter the soil N cycling processes in subalpine forest ecosystems.

Liming and grazing intensities effects on soil mineral nitrogen throughout the pasture cycle in a subtropical integrated crop-livestock system

Grazing intensity is a preponderant factor for the success of integrated crop-livestock systems (ICLS). Management of grazing intensity impacts soil organic matter (SOM) dynamics, soil reacidification process, and amount and quality of residues added to the ICLS. Consequently, the soil mineral nitrogen (N) forms may present different behavior throughout the pasture cycle, because they are directed linked to SOM and soil acidity dynamics. This study aimed to evaluate the impact of grazing intensities and liming in the temporal variation [...]

Activation effect of soil available nitrogen, manganese and cobalt after addition of different fumigants

Soil fumigation is a well-established method for controlling soil-borne diseases. Better quantification of soil available nitrogen and trace elements may provide recommendations on the safe and effective application of soil fumigants. The effects of four fumigants on the available soil nitrogen and trace elements (including Mn, Co, Ni, Cu, Zn and Cd) were investigated in the laboratory incubation with agricultural soil. The results showed that soil fumigation increased soil mineral nitrogen and available Mn, Co, Ni. A significant increase of soil NH4 +-N and available Mn was observed in all fumigation treatments. Chloropicrin treatments showed the largest increase of soil NH4 +-N. In addition, chloropicrin and dazomet increased Mn and Co to a greater extent than dimethyl disulfide and 1,3-dichloropropene in soil. Available Mn content after chloropicrin fumigation has increased by 2.2 times compared with control treatments, and available Co content in dazomet treatments is also 2.8 times more than untreated control. In fumigated soil, the steady increase of soil available elements is beneficial to nutrient uptake by plants. Soil fumigation created an activation effect on soil mineral nitrogen and available trace elements, which may increase their bioavailability to plants and promote plant growth.

Ethnobotanical Uses, Chemical Constituents, and Application of Plantago lanceolata L.

The medicinal benefits of P. lanceolata L. have been acknowledged worldwide for hundreds of years. The plant is now distributed worldwide, especially in temperate zones. This review gives an overview of ethnomedicinal use, phytochemistry, pharmacological activities, and other potential application of P. lanceolate L. Several effective chemical constituents such as polyphenols, tannins, flavonoids, alkaloids, terpenoids, iridoid glycosides, fatty acids, and polysaccharides are found in P. lanceolata L., which contribute to its exerting specific therapeutic effects. Correspondingly, studies have found that P. lanceolata L. has different biological activities, including antioxidant, antibacterial, wound-healing, anti-inflammatory, cytotoxic, and antiulcerogenic activity. The plant also treats various diseases related to the skin, respiratory organs, digestive organs, reproduction, circulation, cancer, pain relief, and infections. The plant has many applications in cosmetics such as lotion and creams; it is also used as an excellent indicator to know the presence and absence of heavy metals and the accumulation in industrial and urban areas. The plant suppresses soil nitrogen mineralization in agriculture due to allelochemicals such as aucubin. The biological activities, medicinal properties, and industrial application of P. lanceolata mainly depend on the activities of the responsible, active chemical constituents. However, this field still needs more study to determine the exact mechanisms and the main bioactive compound activity accountable for these activities. Also, most of the studies have been performed in vitro, so further in vivo studies are recommended for the future.

Modeling the interinfluence of fertilizer-induced NH<sub>3</sub> emission, nitrogen deposition, and aerosol radiative effects using modified CESM2

Abstract. Global ammonia (NH3) emission is expected to continue to rise due to intensified fertilization for growing food to satisfy the increasing demand worldwide. Previous studies have focused mainly on estimating the land-to-atmosphere NH3 injection but seldom addressed the other side of the bidirectional nitrogen exchange – deposition. Ignoring this significant input source of soil mineral nitrogen may lead to an underestimation of NH3 emissions from natural sources. Here, we used an Earth system model to quantify NH3-induced changes in atmospheric composition and the consequent impacts on the Earth's radiative budget and biosphere as well as the impacts of deposition on NH3 emissions from the land surface. We implemented a new scheme into the Community Land Model version 5 (CLM5) of the Community Earth System Model version 2 (CESM2) to estimate the volatilization of ammonium salt (NH4+) associated with synthetic and manure fertilizers into gaseous NH3. We further parameterized the amount of emitted NH3 captured in the plant canopy to derive a more accurate quantity of NH3 that escapes to the atmosphere. Our modified CLM5 estimated that 14 Tg N yr−1 of global NH3 emission is attributable to fertilizers. Interactively coupling terrestrial NH3 emissions to atmospheric chemistry simulations by the Community Atmospheric Model version 4 with chemistry (CAM4-chem), we found that such emissions favor the formation and deposition of NH4+ aerosol, which in turn influences the aerosol radiative effect and enhances soil NH3 volatilization in regions downwind of fertilized croplands. Our fully coupled simulations showed that global-total NH3 emission is enhanced by 3.3 Tg N yr−1 when 30 % more synthetic fertilizer is used compared to the 2000-level fertilization. In synergy with observations and emission inventories, our work provides a useful tool for stakeholders to evaluate the intertwined relations between agricultural trends, fertilizer use, NH3 emission, atmospheric aerosols, and climate so as to derive optimal strategies for securing both food production and environmental sustainability.

How Does Crop Rotation Influence Soil Moisture, Mineral Nitrogen, and Nitrogen Use Efficiency?

Rice–wheat (RW) cropping systems are integral to global food security. Despite being practiced for decades, Chinese RW cropping systems often suffer from low productivity and poor nitrogen use efficiency (NUE), reflecting management approaches that are not well-contextualized to region and season. Here, we develop the best management guides for N fertilizer in RW systems that are designed to help raise the productivity, NUE, and environmental sustainability of winter wheat over the long term. 2-year field experiments were conducted with four N fertilizer rates (0, 135, 180, and 225 kg N ha–1), allowing contrasts of yields, soil moisture, and NUE of wheat in RW in the humid climates zones on the Jianghan Plain. We compared RW systems with soybean/maize dryland wheat (DW) systems that are similarly endemic to China: after soybean/maize is harvested, soils are often drier compared with moisture content following rice harvest. With high seasonal N application rates (180–225 kg N ha–1), wheat crop yields increased by 24% in RW which were greater than comparable yields of wheat in DW, mainly due to greater kernels per spike in the former. Across treatments and years, N accumulation in plant tissue and kernel dry matter of DW was higher than that in RW, although mean agronomic efficiency of nitrogen (AEN) and physiological efficiency of nitrogen (PEN) of RW systems were greater. As N application rates increased from 135 to 225 kg ha–1, AEN and PEN of DW decreased but changed little for RW. Soil ammonium N was much lower than that of nitrate N; changes in NH4+ and NO3– as a consequence of increasing N fertilization were similar for RW and DW. We recommend that tactical application of N fertilizer continue seasonally until midgrain filling for both the DW and RW systems. At fertilization rates above 180 kg N ha–1, yield responses disappeared but nitrate leaching increased significantly, suggesting declining environmental sustainability above this N ceiling threshold. Collectively, this study elicits many functional and agronomic trade-offs between yields, NUE, and environmental sustainability as a function of N fertilization. Our results show that yield and NUE responses measured as part of crop rotations are both more robust and more variable when derived over multiple seasons, management conditions, and sites.

Improving the AquaCrop model to achieve direct simulation of evapotranspiration under nitrogen stress and joint simulation-optimization of irrigation and fertilizer schedules

Water and fertilizer management strategy profoundly influences crop yield, water and nitrogen use efficiency. In this study, a framework for joint simulation-optimization of irrigation and fertilizer schedules (JSOIFS) was established by coupling the improved AquaCrop model, W*N-Jensen model and multi-objective programming. Firstly, the AquaCrop model was modified to simulate evapotranspiration (ET) under nitrogen stress through introducing the concept of shoot actual, critical and minimal nitrogen concentration. The accuracy and applicability of the improved AquaCrop model to simulate ET were verified, taking seed maize of Shiyanghe River Basin as a case. On the basis, an optimization model with the objective of maximum yield calculated by W*N-Jensen model and water use efficiency was developed under the scenarios of different levels of available water and nitrogen, and initial soil mineral nitrogen content. Results showed that the improved model can simulate canopy cover (CC) and ET well with and without water stress. Meanwhile, the precision for CC, biomass, ET and yield of seed maize can be guaranteed when water and nitrogen stress coexist. It indicated that the improved model can be used for irrigation and fertilizer management. The optimal irrigation and fertilizer schedules pointed out that the irrigation and nitrogen application, and initial soil mineral nitrogen all have significant effects on yield. In low fertility soils, irrigation should be concentrated during tasseling stage and fertilization is as critical as irrigation. Conversely, in high fertility soils, irrigation should be dispersed throughout the growth period. Water and nitrogen use efficiency have been promoted compared with the status quo. The recommended water and nitrogen application for seed maize are 150–200 mm and 100–150 kg N/ha, respectively, in study area with the mean soil mineral nitrogen of 182 kg N/ha. The improvement of ET simulation performance of AquaCrop model under simultaneous stress of water and nitrogen provides convenience for achieving precise crop management. Meanwhile, the JSOIFS framework realizes the efficient irrigation and fertilizer schedules in arid areas, improves the resources use rate, and is equally applicable to other regions with the same goals.

Crop Residue Management Strategies to Reduce Nitrogen Losses during the Winter Leaching Period after Autumn Spinach Harvest

In open-field vegetable production, high quantities of soil mineral nitrogen (Nmin) and N-rich crop residues often remain in the field at harvest. After the harvest of crops in autumn, this N can lead to considerable nitrate (NO3−) losses during the subsequent winter leaching period. In four field trials, different tillage depths (3–4, 10, 30 cm) and dates (early autumn, late autumn, early spring) were investigated to reduce N losses after growing spinach in the autumn. In a further treatment, the nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) was directly applied to the crop residues. Potential N losses were calculated by a balance sheet approach based on Nmin concentration (0–90 cm), measured N mineralization and N uptake by catch crops. By postponing the tillage date from early to late autumn or spring, resprouting spinach stubbles acted as a catch crop, reducing N losses by up to 61 kg ha−1. However, if the spinach biomass collapsed, the N losses increased by up to 33 kg ha−1 even without tillage. The application of DMPP as well as the tillage depth were less effective. Overall, postponing tillage to spring seems to be the most promising approach for reducing N losses during the off-season.

P is for persistence: Soil phosphorus remains elevated for more than a decade after old field restoration.

Understanding constraints to ecological restoration on former agricultural land has become increasingly important due to agricultural land degradation in the developed world, and growing evidence for enduring agricultural legacies that limit native species recovery. In particular, the removal of native plant biomass and subsequent disturbance of soil properties through farming activities can alter soil ecosystem processes. Planting of native plant species is a common approach to restoring native vegetation on agricultural land and is assumed to benefit soil ecosystem processes, but the degree to which altered soil chemical processes recover is poorly documented. We investigated recovery of soil chemical properties after restoration in semiarid Western Australia, hypothesizing that elevated nutrient concentrations would gradually decline post planting, but available phosphorus (P) concentrations would remain higher than reference conditions. We used a space-for-time substitution approach, comparing 10 planted old field plots with matched fallow cropland and reference woodlands. Sampling on planted old fields and reference woodland plots was stratified into open patches and under tree canopy to account for consistent differences between these areas. The most prominent legacy of cropping was significantly and substantially higher concentrations of soil available P in fallow croplands and restored old fields compared with reference woodlands. Soil mineral nitrogen (N) concentrations were elevated in fallow croplands compared to open patches in reference woodlands (ammonium and nitrate) and under the tree canopy (ammonium). However, in restored old fields, mineral N concentrations were similar to woodland sites, providing evidence for amelioration over time. No significant differences in nutrient concentrations under tree canopies compared with open patches had developed in the planted old fields, despite a distinction between open patches and he under ttree canopy in reference woodlands for total N. We conclude that soil P legacies in old fields may inhibit the recolonization of native species that are sensitive to, or uncompetitive at, elevated P concentrations. To achieve full recovery, further research is required to test restoration practices aimed at reducing soil P concentrations to facilitate native plant establishment and persistence.

Morphological response of weed and crop species to nitrogen stress in interaction with shading

AbstractReducing herbicide use may result in residual weed flora in arable fields, increasing crop–weed competition for resources. In temperate cropping systems, light and nitrogen are the main resources for which plants compete. As weed competition increases, soil mineral nitrogen might become less abundant as the use of mineral fertiliser is reduced for environmental reasons (pollutions and biodiversity loss). Better understanding crops and weeds competitive abilities for nitrogen and light might help manage weeds and promote weed biological regulation by sowing more competitive crops. Our objectives were to (1) quantify the diversity in species morphological response to nitrogen stress, in interaction with shading and (2) investigate relationships between species responses and species features (clade, crop vs. weed, Ellenberg indexes). Response of three aboveground variables, important for light competition, (specific leaf area [SLA], leaf to aboveground biomass ratio [LBR] and height per unit aboveground biomass [HBR]) to nitrogen stress was measured on four crops and four weeds grown in a greenhouse under various nitrogen treatments and two light levels. Increasing SLA, LBR and HBR in response to nitrogen stress improve plant light competitiveness in a situation of nitrogen deficiency. SLA decreased in response to nitrogen stress for all species, with a higher decrease for nitrophilic species. LBR response to nitrogen stress varied between crops and weeds, weeds decreasing LBR while crops tended to increase it. HBR was independent of nitrogen stress for most species. Shading had a small to no effect on the morphological response to nitrogen stress. These results suggest that the investigated parameters characterise species intrinsic response of morphological variables to nitrogen stress. In the next future, integrating these species properties into a mechanistic model and performing simulations will allow drawing generic conclusions on species competitiveness in various situations.

Effects of Biochar Addition on Soil Nitrogen Mineralization and Leaching Characteristics in Riparian Zone of Taihu Lake

Nitrogen mineralization in riparian soil changes the migration and utilization efficiency of nitrogen, which is closely related to the control of water eutrophication. The differences in soil properties caused by land use alter nitrogen retention and transport capacity. Therefore, the soil of three land use types (woodland, grassland, and cultivated land) in the western riparian zone of Taihu Lake were selected for research on the dynamic changes in nitrogen mineralization amount using an incubation experiment and a leaching characteristics by soil column leaching experiment, and their environmental effects were also studied under different biochar addition conditions (0%, 1%, and 5%). The results showed that, in general, the addition of biochar inhibited nitrogen mineralization in forest land and grassland soil, whereas the effect of biochar on nitrogen mineralization in cultivated land was promoted in low concentrations but inhibited in high concentrations. Leaching experiments showed that the biochar addition reduced the loss of soil mineral nitrogen, and the reduction rate in ammonia nitrogen was 23.28%-39.79%, whereas there was little difference between the three land use types. The nitrate decreased by 17.20%-44.49%, and the reduction rate of cultivated land was smaller than that of forest land and grassland. In conclusion, the input of biochar into grassland and cultivated land can better maintain soil fertility and reduce soil nitrogen loss in riparian soil.

Use of Digestate as an Alternative to Mineral Fertilizer: Effects on Soil Mineral Nitrogen and Winter Wheat Nitrogen Accumulation in Clay Loam

Knowledge of the mineralisation and nutrient release of organic fertilisers is essential to ensure plant nutrient demand and availability, to increase N use efficiency and to minimise environmental risks. In 2018–2020, two similar field experiments were carried out on clay loam Cambisol with winter wheat (Triticum aestivum L.) grown without N application and applying liquid anaerobic digestate (LD), pig slurry (PS) and ammonium nitrate (AN) fertilizer with and without additional fertilization (N120 and N120+50). The aim of the research was to compare the effect of organic and mineral fertilizers on the variation of soil mineral nitrogen forms in the 0–30, 30–60 cm soil layers and N accumulation in wheat yield. Fertilizers applied during the previous growing season increased the nitrate and ammonium nitrogen (N-NO3 and N-NH4) content after the resumption of winter wheat vegetation. The dry period in spring (2019) had a negative impact on winter wheat N uptake. In a year of normal moisture content (2020), PS and LD fertilizers and the fertilizer application of the previous year (2019) significantly increased the N-NO3 content in the topsoil, while all applied fertilizers increased it in the deeper soil layer (by a factor of between 3.6 and 12.3), compared to unfertilized soil.

Single midseason drainage events decrease global warming potential without sacrificing grain yield in flooded rice systems

Rice (Oryza sativa L.) cultivation is an important part of global food security, yet it is also responsible for a significant portion of agricultural greenhouse gas (GHG) emissions, particularly methane (CH4). Midseason drainage of flooded rice fields can decrease CH4 emissions, but the magnitude of CH4 reduction and its effect on grain yield are variable due to variation in the timing and soil-drying severity of drainage across studies. Therefore, in this two-year study, we aimed to quantify the effect of timing and severity of a single midseason drainage event on seasonal GHG emissions and grain yields, compared to a continuously flooded (CF) control. Treatments varied in terms of soil-drying severity (low, medium, and high, corresponding to approximately 5, 8, and 12 days of drying, respectively) and the timing of when drainage events occurred (between 34–49 and 45–59 days after seeding, or roughly between tillering and panicle initiation). Soil moisture parameters (perched water table, volumetric water content, gravimetric water content (GWC), and soil water potential), soil mineral nitrogen, CH4 and nitrous oxide (N2O) emissions, grain yield, and yield components were all quantified. Midseason drainage reduced seasonal CH4 emissions by 38–66%, compared to the CF control. Seasonal CH4 emissions decreased with increasing drain severity, and for every 1% reduction in soil GWC during the drainage period, seasonal CH4 emissions were reduced by 2.5%. The timing of drainage had no significant impact on CH4 emissions. Emissions of N2O were low (average = 0.035 kg N2O-N ha−1) and accounted for only 0.5% of the seasonal global warming potential (GWP) across all drainage treatments. Within each year, drainage did not significantly affect grain yield compared to the CF control. Additionally, midseason drainage reduced both GWP and yield-scaled GWP by approximately the same amount as seasonal CH4 emissions, as N2O emissions were minimal and yields were similar across treatments. These results indicate that midseason drainage may be a viable GHG mitigation practice in flooded rice systems with limited risk for yield reduction, however, this practice should also be further tested under a broad range of soil types and different environments to determine its widespread adoptability.

Optimizing nitrogen fertilizer inputs and plant populations for greener wheat production with high yields and high efficiency in dryland areas

Bridging yield gaps in staple crops is widely reported as a highly efficient means for improving grain production. However, changes in production efficiency and the environmental footprint remain less investigated when narrowing these gaps. In this study, we collected data from 299 wheat plots on the Loess Plateau of China to identify changes in nitrogen efficiency, nutrient balance, and environmental risks when narrowing the yield gaps. The low-yielding (LY) and high-yielding (HY) plots had an average yield gap of 1936 kg ha–1 (33.5%) and nitrogen partial factor productivity gap of 10.3 kg kg–1 (30.1%) that were simultaneously narrowed under similar fertilizer inputs. Optimizing sowing date improved spikes per m2 (27.4%) and grains per head (12.9%), key measures to improving wheat grain yields. The high-yielding high-efficiency (HYHE) plots produced on average 43.0% and 14.6% higher nitrogen partial factor productivity and grain yield, respectively than the high-yielding low-efficiency (HYLE) plots. Appropriate nitrogen fertilizer inputs significantly enhanced nitrogen use efficiency and maintained grain yield on HY plots. Grain yield and nitrogen partial factor productivity gradually increased with year of cultivar release (1995–2019) (P < 0.05). However, soil organic matter, pH, available phosphorus, mineral nitrogen, and available potassium had no significant effect on grain yield or nitrogen use efficiency. The HYHE plots had the lowest nitrogen surplus (25 kg N ha–1), phosphorus surplus (31 kg P ha–1), and greenhouse gas emissions (2327 kg CO2-eq ha–1) of the surveyed plots. In the HY plots, moderate potassium fertilizer should be supplemented to balance wheat production. In conclusion, excellent cultivars and high plant density are key for bridging the yield gap between LY and HY plots. Optimizing fertilizer management could further promote HY plots from low to high production efficiency. This research provides farmers with the knowledge and methods to sustainably bridge field-level yield gaps in dryland wheat production.

Changes in soil bacterial communities and nitrogen mineralization with understory vegetation in boreal larch forests

Plant community composition can alter soil microbial community structure and function, and further influence the process of soil N transformation. However, this effect is rarely noticed in forest types characterized by understory vegetation, especially in N-limited boreal forests where the understory vegetation substantially contributes to soil nutrient cycling. To investigate whether forest types characterized by understory vegetation can affect soil N mineralization and bacterial community, we determined mineral N contents, net N mineralization rates, soil bacterial community and microbial biomass in soils under three types of larch forest (Sphagnum-Bryum-Rhododendron tomentosum (previously: Ledum palustre)-Larix gmelinii forest(SLL), Rhododendron dauricum-Larix gmelinii forest (RL), and Rhododendron tomentosum-Larix gmelinii forest (LL)) in the typical boreal climatic region in northeast China. We found that soil N availability, soil N mineralization rates, soil bacterial community and microbial biomass vary with the difference of the understory vegetation, and these changes were stronger in the 0–10 cm soil layer than in the 10–20 cm soil layer. In addition, compared with soil N content, soil microbial biomass was more strongly correlated with soil N mineralization. Structural equation modeling was used to analyze the effects of driving factors and pathways on soil N dynamics. The results suggested that soil N mineralization was related to forest type and soil microbial biomass, while soil microbial biomass was significantly affected by soil bacterial composition. Finally, abundances of Actinobacteria, Patescibacteria and Chloroflexi were significantly correlated with soil N mineralization. Together, these mechanisms provide insight into the important function of understory vegetation in the process of soil N cycling in the boreal region.

Liming and Phosphate Application Influence Soil Carbon and Nitrogen Mineralization Differently in Response to Temperature Regimes in Allophanic Andosols

Andosols are characterized by high organic matter content and play a significant role in carbon storage. However, they have low phosphorus fertility because of the high phosphate-fixing capacity of active aluminum. For agricultural use of Andosols, it is necessary to ameliorate its poor phosphorus fertility by applying lime and high doses of phosphate fertilizers. The objective of the present study was to clarify how such soil amendments affect the mineralization of soil organic carbon (C) and nitrogen (N) in allophanic Andosols under different temperature regimes. The soil was treated using combinations of liming and heavy phosphate application, followed by incubation under different temperature conditions. The N mineralization and the soil CO2 evolution rate were measured periodically. The patterns of N mineralization were analyzed by fitting them to first-order kinetics. Liming increased C and N mineralization irrespective of temperature, and the increase was further enhanced by phosphate application. Kinetic analysis of the N mineralization curve indicated lowering of the activation energy of N mineralization reactions with phosphate application, suggesting that P application may accelerate N mineralization at lower temperatures. These findings provide a basis for developing soil management strategies to reduce the loss of soil organic matter.

Carbon dioxide emission, nitrogen mineralisation and spinach dry matter yield in a loamy humic soil amended with lime and poultry manure.

While application of lime and poultry manure (PM)increase availability of mineral N inacidic humic soils (> 1.8% organic carbon), these amendments enhance decomposition of soil organic carbon (SOC) increasing carbon dioxide (CO2) emissions. This study investigated the effects of co-application of PM and lime on (i) CO2 emission, (ii) concentration of mineral-N and (iii) spinach dry matter yield and nutrient uptake in a humic soil. Two incubation experiments were set up for 84days to determine (i) CO2 emission and (ii) mineral-N on soils fromthe 0-10- and 10-20-cm depths. The treatments were PM (10 t ha-1), lime (12 t ha-1), PM + lime and unamended control. Same treatments (with inclusion of inorganic fertilisers) were applied to a pot trial using soils (0-10-cm depth) that were pre-incubated for 0, 14 and 35days before planting spinach, and dry matter yield and N uptake were determined. Co-application of PM and lime significantly decreased ammonium-N in soilat both depths but increased nitrate-N and CO2 emission than lime alone. Poultry manure significantly increased ammonium-N and CO2 emission at 0-10-cm depth. For all treatments, cumulative CO2-C was significantly higher at 0-10cm. Dry matter yield for PM + lime and lime + mineral N was higher than when separately applied. Pre-incubation of soils with lime and PM, separately or in combination, increased dry matter yield. These findings imply that application of PM and lime in humic soils increases mineral-N availability and crop productivity, especially when pre-incubated for 35days, whilst the increase in CO2 emission could result in the decrease of SOC.

Hardwood mixtures facilitate leaf litter decomposition and soil nitrogen mineralization in conifer plantations

Productivity in conifer plantations can be increased by hardwood mixture. However, the underlying mechanisms that govern the relationship between hardwood mixture and productivity remain poorly understood, particularly with respect to nutrient cycling. We investigated how and to what extent hardwood mixtures alter nitrogen amounts in leaf litterfall, leaf litter decomposition rates, and soil nitrogen mineralization rates in an experiment that used different thinning intensities (i.e., a non-thinned “control” group with few hardwoods, a 33%-thinned “weak” group with a small amount of hardwoods, and a 67%-thinned “intensive” group with abundant hardwoods) in a conifer Cryptomeria japonica plantation (38-year old). Most of the hardwoods were 15-year old trees that have been regenerated after the first thinning. The annual leaf litterfall amount for the conifer was highest in the control group and lowest in the intensive group, whereas the reverse was true for hardwoods, although the hardwoods’ annual leaf litterfall amount was approximately half that of conifers, even in the intensive group. Consequently, the annual amount of leaf litterfall of hardwoods and conifers combined was lowest in the intensive group. However, the total amount of nitrogen in the annual leaf litterfall of hardwoods and conifers combined did not differ according to thinning intensity, because the mass-based nitrogen concentration in the leaf litterfall of hardwoods was twice that of conifers. The leaf litter decomposition rate in hardwoods was approximately three times faster than that in conifers irrespective of thinning intensity, mainly due to the lower carbon-to-nitrogen (C:N) ratio. Thus, the total amount of nitrogen in the decomposed leaves of hardwoods and conifers combined, calculated by multiplying the total amount of nitrogen in the annual leaf litterfall of hardwoods and conifers by the decomposition rate and summing the results, was highest in the intensive group. In soil from shallow depths (0–10 cm), the nitrogen mineralization rate increased in the order of control, weak, and intensive, attributable primarily to the C:N ratio, which decreased in the same order. The results indicated that increasing the hardwood content by intensive thinning significantly enhances the availability of soil inorganic nitrogen in conifer plantations, by facilitating leaf litter decomposition and soil nitrogen mineralization. These findings indicate that hardwood mixtures can increase forest productivity by enhancing nitrogen cycling.

Linking Phyllostachys edulis (moso bamboo) growth with soil nitrogen cycling and microbial community of plant-soil system: Effects of plant age and niche differentiation

Understanding the impacts of plant age on bamboo growth, soil nutrient and functional microorganism can assist in the development of management practices to maximize the benefits of nutrients and functional endophytic and soil microbes in moso bamboo plantations. In this study, moso bamboos of different ages (0.5, 2.5, 4.5 and 6.5 years) were selected. The above-ground biomass, soil properties and endophytic microbes of above-ground tissue and stump root of different age bamboos were quantified, and their interactive relationships were also examined. There were negligible differences in the heights and above-ground fresh biomass among the bamboo plants of different ages, but net nitrogen (N) mineralization and potential nitrification rates of soils were significantly affected by the bamboo ages. The soil nprA gene abundances decreased with the bamboo ages, and soil AOB amoA gene abundances of the 0.5-yr bamboo were significantly higher than those of the other older plants. Average soil urease activities of the 2.5-yr, 4.5-yr and 6.5-yr bamboos were 81.4%, 81.1% and 88.2% lower than those of the 0.5-yr bamboo, respectively. Bacterial diversity indices and richness estimators in the soils were significantly higher than those in the above-ground tissues. Endophytic microbial community structures were more sensitive to the bamboo ages than the soil counterparts, and endophytic microbial community diversities and structures in the above-ground tissues were significantly changed with the bamboo ages. Bacterial and fungal community structures in the above-ground tissues were significantly different from those in the soils. Bamboo ages significantly affected the N transformations in the soils and endophytic community structures, but niche differentiations among the above-ground tissue, stump root and soil outweighed the plant ages in shaping the whole microbial communities of plant-soil system.

Ecosystem Services Provided by Cover Crops and Biofumigation in Sunflower Cultivation

In south-western France, sunflowers are usually grown in short rotations and after a long fallow period during which soils are left bare. This practice can favour diseases, caused by soilborne fungi, such as sunflower verticillium wilt (SVW), as well as nitrate leaching, both of which can decrease yields. Growing cover crops during a fallow period is an agroecological practice that could provide ecosystem services and mitigate SVW. A Brassicaceae cover crop that causes biofumigation produces glucosinolates and liberate biocidal compounds that might regulate SVW biologically. Moreover, the green manure effect of the Fabaceae might increase soil mineral nitrogen (SMN). To go further, mixtures of Brassicaceae and Fabaceae might mutualise the benefits that each cover crop has in sole crops. A four-year field study in south-western France tested Brassicaceae (brown mustard, turnip rape and fodder radish) and Fabaceae (purple vetch) in sole crops or a mixture with two or three species during the fallow period, followed by biofumigation, and sunflower crop. The cover crops were characterised, SMN was measured, the SVW and yield were assessed and compared to those of the crop grown on soils left bare during the fallow period. Purple vetch as a sole crop cover crop significantly increased SMN before sunflower sowing but only in 2019. Fodder radish as a sole crop reduced SVW severity significantly, overall, 80 days after sowing, except in 2019, when weather conditions were unfavourable to biofumigation. Purple vetch as a sole crop also reduced significantly SVW severity in 2017 and 2020. Finally, sunflower yields after cover crops were higher than those after bare soils, only after purple vetch as a sole crop in 2020, with a mean increase of 0.77 t ha−1. Mixtures of Brassicaceae and Fabaceae sowed at these densities resulted in an intermediate SMN level between those in sole crops and the bare soil and they did not significantly decrease SVW or increase yields. Our results suggest that cover crops, especially fodder radish or purple vetch, and biofumigation can provide ecosystem services for sunflower, instead of leaving soils bare during the fallow period. However, the extent of ecosystem services is markedly affected by soil and climatic conditions as well as other management practices.